1. Field of the Invention
The present invention generally relates to a liquid crystal electro-optical (display) device, and particularly relates to a liquid crystal electro-optical (display) device in which light-interrupting patterns are provided on one of a pair of substrates constituting a liquid crystal panel on which substrate thin-film transistors (TFTs) are formed.
2. Description of the Related Art
The liquid crystal display device is widely used in a projection display apparatus and as a display device of a portable (or lap-top) information processing apparatus. Recently, attempts to use the liquid crystal display device as a high-resolution color display device of a stationary (or desk-top) information processing apparatus have started.
FIG. 10 shows an example of a projection liquid crystal display apparatus. Referring to FIG. 10, light emitted from a high-intensity metal halide lamp 61 is passed through a filter 61a, changed in optical path by a mirror 62, and then partially reflected by a dichroic mirror 63. The light reflected by the mirror 63 is again reflected by a mirror 64, and passed through a condenser lens 65 and a liquid crystal display panel 66. The light outputted from the liquid crystal display panel 66 passes through dichroic mirrors 67 and 68, and reaches a projection lens 69.
On the other hand, part of the light passed through the dichroic mirror 63 is reflected by a dichroic mirror 70, passed through a condenser lens 71 and a liquid crystal panel 72, and then reflected by the dichroic mirror 67. The light reflected by the mirror 67 reaches the projection lens 69 through the dichroic mirror 68.
The light passed through the dichroic mirror 70 is passed through a condenser lens 73 and a liquid crystal display panel 74, then reflected by a mirror 75 and the dichroic mirror 68, and finally projected by the projection lens 69.
Among several types of liquid crystal display devices, the active matrix liquid crystal display device, in which an individual pixel is driven by a thin-film transistor (TFT), is suitable for attaining the above-mentioned high-resolution color display. The active matrix driving method can eliminate crosstalk between pixels which may occur in the passive matrix driving method, and hence can provide superior display performance. In the active matrix driving method, TFTs are arranged on one of the glass substrates that constitute a liquid crystal panel and each TFT controls a voltage applied to a corresponding, transparent pixel electrode.
In the active matrix liquid crystal display device, portions of the liquid crystal layer existing over the pixel electrodes receive drive electric fields generated by means of the TFTs and hence serve for on/off-control of light transmission. However, portions of the liquid crystal layer right above the TFTs are not given any drive electric fields, projection light, back light, or the like may leak through those portions. To improve the display contrast ratio, it is necessary to minimize the light that leaks through the portions where the TFTs are formed. To this end, conventionally, light-interrupting patterns are formed on the substrate that is opposed to the TFT-bearing substrate in the portions where the TFTs are formed. However, in this configuration, precise alignment is needed between the two substrate so that the light-interrupting patterns cover the corresponding TFTs, as a result of which the liquid crystal panel assembling step takes a long time. If wider light-interrupting patterns are formed to facilitate the alignment operation, there arise such problems as a decrease in display brightness.
To solve the above problems, the present inventors investigated a configuration in which light-interrupting patterns are formed on the TFT-bearing substrate, and produced experimental models of such a liquid crystal display device.
FIG. 11 is a plan view of a liquid crystal display panel experimentally produced by the inventors. Referring to FIG. 11, a plurality of generally U-shaped polysilicon patterns 1 are formed corresponding to respective pixels of the liquid crystal display device on one of the two glass substrates opposed to each other to constitute a liquid crystal panel. Connection pads 1a and 1b are formed at both ends of each polysilicon pattern 1. A plurality of aluminum gate bus patterns 2 are formed parallel with each other on the same glass substrate so as to cross over the polysilicon patterns 1 through a SiO2 film serving as a gate insulating film. In each polysilicon pattern 1, the portions on both sides of the portions where the polysilicon pattern 1 crosses the gate bus pattern 2 are doped with an n-type or p-type impurity, so that channel regions of TFTs are formed corresponding to the crossing points of the polysilicon pattern 1 and the gate bus pattern 2. For each U-shaped polysilicon pattern 1, a pair of n-channel or p-channel TFTs are formed so as to be connected to each other in series.
Further, a plurality of aluminum data bus patterns 3 are formed parallel with each other in the vertical direction as viewed in FIG. 11 on the polysilicon patterns 1 so as to correspond to the respective connection pads 1b. Each data bus pattern 3 is connected to the corresponding connection pad 1b via a contact hole, and drive current is supplied via the connection pad 1b to a p-type or n-type drain region that is formed in the polysilicon pattern 1. On the other hand, the connection pad 1a is connected to a transparent pixel electrode through a light-interrupting pattern or an aluminum pattern (described below).
In the above configuration, a light-interrupting mask 5 is formed corresponding to the gate bus patterns 2 and the data bus patterns 3. The light-interrupting mask 5, which is made of an opaque metal such as Ti, interrupts light that leaks through openings between adjacent pixel electrodes.
FIG. 12 is a sectional view taken along line 12-12 in FIG. 11. Referring to FIG. 12, the polysilicon pattern 1 is formed on a glass substrate 10 and covered with a first-layer insulating film 6. The data bus pattern 3 is formed on the insulating film 6, and connected to the connection pad 1b of the polysilicon pattern 1 via a contact hole 6a that is formed through the insulating film 6.
The data bus pattern 3 is covered with a second-layer insulating film 7, and the light-interrupting mask 5 is formed on the insulating film 7 so as to correspond to the data bus pattern 3. The light-interrupting mask 5 is covered with a third-layer insulating film 8, and an ITO pattern 9 as a transparent electrode is formed on the insulating film 8. The transparent electrode pattern 9 is connected to the connection pad 1a of the polysilicon pattern 1 via another contact hole (not shown).
Although not shown in the sectional view of FIG. 12, the gate bus pattern 2 is formed on the substrate 10 in the same level as the polysilicon pattern 1, and crosses over the polysilicon pattern 1 at the channel regions of the TFTs.
In FIG. 11, the data bus pattern 3 is drawn so as to be shifter leftward from the polysilicon pattern 1. This simply indicates that the data bus pattern 3 is formed on the polysilicon pattern 1 as shown in FIG. 12.
In the above configuration, the portions of the light-interrupting mask 5 extending in the vertical direction as viewed in FIG. 11 (i.e., in the column direction) interrupt light that leaks out passing by both side edges of the data bus pattern 3 which extends in the vertical direction. Since the data bus pattern 3 possibly interacts with the transparent electrode pattern 9 via a capacitance, it cannot be made so wide as to overlap the electrode pattern 9; a gap g should necessarily be formed in between. The light interrupting mask 5 interrupts light that leaks through the gap g.
In the configuration of FIGS. 11 and 12, the light-interrupting mask 5 can be formed on the substrate 10 on which the TFTs are formed, by part of a series of steps for forming the TFTs. Therefore, substantially ideal alignment can be attained between the light-interrupting mask 5 and the TFTs, whereby the conventional step of accurately aligning the substrate 10 with the opposed substrate on which a light-interrupting pattern is formed can be omitted.
However, when a liquid crystal display device having the configuration of FIGS. 11 and 12 was actually produced, a problem was found that the metal pattern as the light-interrupting mask 5 was likely short-circuited with the data bus pattern 3, making it difficult to increase the yield of the liquid crystal display device.
This is considered due to a phenomenon that insufficient step coverage of the insulating film 7 with respect to the data bus pattern 3 causes short-circuiting between the light-interrupting mask 5 and the data bus pattern 3, as illustrated in FIG. 13. Similar short-circuiting likely occurs between the light-interrupting film 5 and the transparent electrode pattern 9. Since the light-interrupting mask 5 is a continuous member extending vertically and horizontally as shown in FIG. 11, such short-circuiting causes a line defect.
A general object of the present invention is to provide a novel, useful liquid crystal electro-optical (display) device that is free of the above-described problems.
A specific object of the invention is to provide a liquid crystal electro-optical (display) device in which a light-interrupting mask can be aligned easily and which is high in both reliability and yield.
To attain the above objects, according to the invention, there is provided a liquid crystal electro-optical (display) device comprising a pair of substrates opposed to each other to constitute a liquid crystal panel; a plurality of thin-film transistors arranged in matrix form on one of the pair of substrates so as to correspond to a plurality of pixels, respectively; a plurality of light-interrupting stripes continuously extending parallel with each other in a row direction so as to cover the thin-film transistors arranged in the row direction; and light-interrupting patterns formed corresponding to the respective pixels so as to be isolated from each other and from the light-interrupting stripes.
The light-interrupting pattern may include, for each of the pixels, first and second patterns isolated from each other, the first isolated pattern covering one edge of an associated one of light-interrupting patterns extending in a column direction which constitute data bus patterns for the thin-film transistors, the second isolated pattern covering the other edge of the light-interrupting pattern.
The liquid crystal display device may further comprise a plurality of light-interrupting patterns extending in the row direction which constitute gate bus patterns for the thin-film transistors, each of the gate bus patterns having branches provided corresponding to the respective data bus patterns so as to extend downward in the column direction.
The light-interrupting stripes may be formed so as to cover the respective gate bus patterns, and a tip of each of the branches may be located outside a side edge of the associated light-interrupting stripe.
Each of the light-interrupting stripes may have branches extending in the column direction so as to cover the respective data bus patterns.
According to another aspect of the invention, there is provided a liquid crystal electro-optical (display) device comprising a pair of substrates opposed to each other to constitute a liquid crystal panel; a plurality of thin-film transistors arranged in matrix form on one of the pair of substrates so as to correspond to a plurality of pixels, respectively; a plurality of light-interrupting stripes formed on one of the substrates carrying the thin film transistors; and continuously extending parallel with each other in a column direction so as to cover the thin-film transistors arranged in the column direction; and light-interrupting patterns formed corresponding to the respective pixels so as to be isolated from each other and from the light-interrupting stripes.
The light-interrupting pattern may include, for each of the pixels, first and second patterns isolated from each other, the first isolated pattern covering one edge of an associated one of light-interrupting patterns extending in a row direction which constitute gate bus patterns for the thin-film transistors, the second isolated pattern covering the other edge of the light-interrupting pattern.
According to a further aspect of the invention, there is provided a liquid crystal electro-optical (display) device comprising a pair of substrates opposed to each other to constitute a liquid crystal panel; a plurality of thin-film transistors arranged in matrix form on one of the pair of substrates so as to correspond to a plurality of pixels, respectively; and a plurality of light-interrupting stripes continuously extending parallel with each other in a row direction so as to cover the thin-film transistors arranged in the column direction, each of the plurality of light-interrupting stripes having branches extending in a row direction so as to cover respective gate bus patterns for the thin-film transistors extending in the row direction, one of the branches of each of the light-interrupting stripes being opposed to the corresponding branch of the adjacent one of the light-interrupting stripes above a semiconductor pattern as an active portion of the associated thin-film transistor to form a gap narrower than a width of the semiconductor pattern.
In each of the above liquid crystal electro-optical (display) devices, the plurality of light-interrupting stripes may be connected to a common potential.
The principle of the present invention will be described below with reference to FIGS. 1, 3 and 4. FIG. 1 is a plan view showing a basic layout of a liquid crystal electro-optical (display) device according to the invention, and FIGS. 3 and 4 are sectional views taken along lines 3-3 and 4-4 in FIG. 1, respectively.
Referring to FIG. 1, in the invention, a plurality of light-interrupting stripes 5xe2x80x2 are formed so as to extend in the row direction instead of the light-interrupting mask 5 shown in FIG. 11. Further, branches 2A are formed so as to extend from a gate bus pattern 2 in the column direction as light-interrupting patterns for data bus patterns 3 extending in the column direction. Each branch 2A does not reach the adjacent polysilicon pattern 1 and a gap is formed with a connection pad 1b of the polysilicon pattern 1. Therefore, the gate bus pattern 2 and the polysilicon pattern 1 never contact with each other electrically via the branch 2A.
In the invention, to prevent leakage of light through the above-mentioned gap, first and second light-interrupting patterns 5A and 5B are formed so as to be isolated from the light-interrupting stripe 5xe2x80x2. Made of an opaque metal as in the case of the light-interrupting stripe 5xe2x80x2, the light-interrupting pattern 5A prevents light leakage through the gap between the left side edge of the data bus pattern 3 and a transparent electrode pattern 9. Similarly, the light-interrupting pattern 5B prevents light leakage through the gap between the right side edge of the data bus pattern 3 and an adjacent transparent electrode pattern 9 on the right.
In the above configuration, should the light-interrupting pattern 5A or 5B short-circuit with the data bus pattern 3, the short-circuiting does not affect display because the light-interrupting patterns 5A and 5B are isolated. Therefore, the invention provides a liquid crystal electro-optical (display) device which can attain high-contrast display with sufficient light interruption without causing a line defect.